The invention concerns a monobloc intraocular lens made of a flexible material which can be rolled or folded, but which is sufficiently elastic for the lens to regain, after being implanted in an ocular housing, a functional shape corresponding to its initial shape, namely exhibiting a shape memory.
Former generations of intraocular lenses were made of a rigid material (such as PMMA) and, in order to be implanted in the eye, a large incision had to be made in the cornea (usually of the order of 6 mm corresponding to the diameter of the optic part of the lens) which presented many disadvantages (post-operative astigmatism, greater risks of surgical complications etc).
In order to overcome these disadvantages, lenses have been proposed made of a flexible material such as silicone or materials described as xe2x80x9chydrogelsxe2x80x9d, or xe2x80x9cacrygelxe2x80x9d, or xe2x80x9cacrylicxe2x80x9d (this term having a different meaning from its common one) which are PMMAs (polymethylmethacrylate) and/or HEMA (hydroxyethylmethacrylate) hydrated to more than 16%, in particular between 24% and 28%. These lenses can be folded or rolled and can be implanted through a smaller incision, in particular through the incision made in order to introduce an instrument into the eye necessary for prior surgical treatment (for example a 3 mm to 3.5 mm incision for ablation of the crystalline lens by phacoemulsification).
Nevertheless, the flexibility of this material then presents the problem of the mechanical stability of the lens after implantation. In particular, in the case of capsular lenses, since the capsular sac has initially a diameter of the order of 10 to 11.5 m, it retracts radially after ablation of the crystalline lens, to a diameter of the order of 9.5 mm or even less.
In order to oppose this retraction, bicomponent lenses have been proposed of which the optic part is flexible while the haptic parts are made of rigid PMMA. These lenses have a complex structure and there is a risk of their flexible optic part deforming under the effect of radial stresses transmitted by the rigid haptic parts.
On the other hand, monobloc lenses have been proposed made of a flexible material, designed to be adapted to radial deformations of the ocular housing. In particular, monobloc lenses are known (EP-579 528) made of a flexible material comprising a central optic part in the shape of a disc defining a principal plane of the lens and a haptic part comprising:
two loops, so-called contact loops, designed to come into contact with an inner wall of the eye, each of these contact loops having the general shape of a convex circular arc, with a convexity directed outwards radially with respect to the optic part, these contact loops being both inscribed in the same circle with a diameter of the order of 11 mm,
for each contact loop, two linking elements extending between the optic part and the contact loop, the lens having, seen in plan, and before implantation, an initial shape which is symmetrical overall with respect to the two perpendicular axes of symmetry contained within the principal plane.
Nevertheless, phenomena of angular displacements (tilt) and/or axial displacements and/or radial displacements (eccentricity) and/or deformations, in particular bending movements, are also sometimes noticed with these lenses after implantation.
Certain monobloc lenses have also been proposed having the haptic parts tilted with respect to the principal plane of the optic part, so that deformations can occur in flexion perpendicular to this principal plane. Nevertheless, with these lenses, the risk of premature displacement and/or deformation phenomena is not overcome. Moreover, these tilted lenses present a not inconsiderable risk of error in positioning the axial direction. Indeed, the relatively small direction of tilt is virtually undetectable by the surgeon, taking into account in particular the flexibility of the material. In addition, since the lens is folded and/or rolled when implanted, an error is possible in assessing the direction of deployment of the lens.
The object of the invention is to overcome these disadvantages, by providing a monobloc intraocular lens made of a flexible material with a shape memory which can adapt to radial retraction of the ocular housing in which it is implanted without risk of premature displacements or deformations of the optic part.
The object of the invention is more particularly to provide a monobloc intraocular lens of which the haptic part is deformable radially so as to be adapted to the radial retraction of the ocular housing, in particular for the capsular sac with a value of the diameter of the order of 9.5 mm, but which can reach a diameter of the order of 8.5 mm, the optic part remaining in the same principal plane, the symmetries of the lens being at least substantially preserved during deformations of the haptic art (under the effect of stresses which are assumed to be uniformly distributed), the optic part remaining centred on the same axis and not undergoing perceptible deformation affecting its optical properties.
The object of the invention is also to provide a lens which is, and remains, perfectly stable in the ocular implantation housing.
The object of the invention is also to provide a lens which can be easily inserted and in particular may be inserted through a smaller incision, in particular 3 to 3.5 mm, the lens being folded and/or rolled, and without the risk of error in the axial direction in which the lens is inserted by the surgeon.
The object of the invention is also to provide a lens which is simple and inexpensive to produce.
The object of the invention is more particularly to provide a posterior chamber lens, in particular a capsular lens, namely one intended to be implanted in the capsular sac or a lens intended to be implanted in the sulcus.
The object of the invention is also to provide a lens which can be applied to an adult as well as to a child.
To this end, the invention concerns a monobloc intraocular lens made of a flexible material which can be folded or rolled, but which is sufficiently elastic so that the lens regains, after being implanted in an ocular housing with a mean diameter equal to xcfx86m, a functional shape corresponding to its initial shape, comprising a central optic part in the shape of a disc having an optical axis and defining a principal plane of the lens perpendicular to the optical axis, and a haptic part comprising
two loops in contact with an inner wall of the eye, each of these contact loops having an external surface with a generally convex-shaped curve with a convexity directed outwards radially with respect to the optic part,
for each contact loop, two linking elements extending between the optic part and the contact loop, the lens having, seen in plan, and before implantation, an initially overall symmetrical shape with respect to the two perpendicular axes of symmetry contained within the principal plane, the so-called horizontal principal axis and vertical principal axis,
the external surface of each contact loop having a trace in the principal plane which is a convex curve defining an apex of intersection with the horizontal principal axis, and two points, referred to as end points, equidistant from the horizontal principal axis between which the radius of curvature is always greater than 2.5 mm,
wherein:
the circle passing through the apex and the two end points of each contact loop has a diameter xcfx86a greater than or equal to xcfx86m and less than xcfx86m+1.5 mm,
the apices of the two contact loops are separated from each other by a distance D different from xcfx86a and greater than xcfx86a,
the linking elements are adapted so that they can be deformed in flexion in the principal plane in the direction of a reduction in the radial dimensions of the lens by bringing the contact loops towards each other and the optic part, while preserving the symmetry of the lens with respect to the two horizontal and vertical principal axes, and at least substantially without deformation or displacement of the optic part, so that the lens can be adapted to a radial retraction of the ocular housing.
In all the text, unless indicated to the contrary, the described geometrical or dimensional characteristics of the lens are those which it has before implantation, i.e. those which correspond d to its initial shape. The lengths and widths are dimensions parallel to the principal plane and the thicknesses are dimensions perpendicular to the principal plane, i.e. parallel to the optical axis of the optic part. xe2x80x9cTrace of a surface in the principal planexe2x80x9d is understood to mean the curve of intersection of this surface and the principal plane.
Advantageously and according to the invention, the contact loops and the linking elements are adapted so that the contact loops can be brought towards each other and the optic part so that the trace of the external surface of the contact loops in the principal plane is circumscribed in a circle with a diameter xcfx86r less than or equal to xcfx86a and greater than xcfx86mxe2x88x921 mm.
Advantageously and according to the invention, each linking element has at least one elbow in the principal plane, and in particular at least one elbow with a convexity directed towards the contact loop, and is adapted so as to be deformable in flexion in the principal plane with a bending axis passing through this elbow. More particularly, advantageously and according to the invention, each linking element has at least one first elbow with a convexity directed towards the contact loop, and at least one second elbow with a concavity directed towards the contact loop.
Advantageously and according to the invention, each linking element is formed of at least one strand of material, referred to as a linking strand, with a width at least substantially constant and a thickness at least substantially constant, and extending between a junction zone with the periphery of the optic part and a junction zone with a contact loop while having at least one elbow in the principal plane. More particularly, advantageously and according to the invention, each linking element is formed of a single linking strand having at least one first elbow with a convexity directed towards the contact loop.
Advantageously and according to the invention, the junction zone of a linking strand with the periphery of the optic part is disposed at least substantially in the extension of a radius of the optic part, this radius forming with the horizontal principal axis, an angle of between 20xc2x0 and 45xc2x0 in particular of the order of 30xc2x0. Moreover, advantageously and according to the invention, each linking strand is linked to a contact loop in a junction zone disposed on a radius of the circle passing through the apex and the two end points, forming with the horizontal principal axis an angle of between 45xc2x0 and 75xc2x0, in particular of the order of 60xc2x0. In addition, advantageously and according to the invention, each linking element is inscribed in an angular sector of which the centre corresponds to that of the optic part and is at least substantially a bisector of the two principal horizontal and vertical axes.
Advantageously and according to the invention, the contact loops and the linking elements extend at least substantially over the principal plane, the lens having zero tilt. Moreover, advantageously and according to the invention, each contact loop is formed of a curved arc with a width which is at least substantially constant extending between the two free ends.
Advantageously and according to the invention, the trace of the external surface of each contact loop in the principal plane is a portion of a circle of diameter xcfx86a. As a variant, this trace may be distinct from a circle and may have a radius of curvature which varies between the apex and the end points, for example it may be conical.
It should be noted that in the prior art, attempts have been made up to now to cause isotropic radial deformations, i.e. those substantially of the same value over all the contact surface of the haptic part with the internal walls of the ocular housing.
On the contrary, in the invention, deformations of the lens include a bringing together in translation of the two contact loops along a preferred direction, namely the horizontal principal axis, on account of the fact that D greater than xcfx86a. It has been proved that this characteristic enables much greater deformation amplitudes to be obtained in practice, which makes it possible to adapt to the capsular retraction, whatever its extent, preventing in this way displacements and deformations of the optic part.
The invention also concerns a lens characterized in combination by all or part of the characteristics mentioned above or hereinafter.